you will need to watch them close - what ive done is open the hive and set the queen cage arcoss the frames above the bees - the bees will come to her- then pick up the queen cage and watch the bees - if they are inserting there tounges to feed her they most likely need her but if the workers are biting at the wire and or trying to sting at her - then id say that have a queen and wish not to have a new one --
you will see the differnce in the hive mood if they have a queen already - its rather more like a riot!!!!
hope this helps
also if you are unsure if you have a queen wait 3-4 days and check for eggs -